Matthew P. Rowe

Voltage-gated sodium channel in grasshopper mice defends against bark scorpion toxin.

Bite Me! As unpleasant as it is, pain serves a purpose, to alert the body to potential damage. This protective function may explain why few predators have evolved resistance to the painful venoms used as a defense by their prey. The grasshopper mouse, however, is insensitive to one of the most painful stings in the animal kingdom—that of the bark scorpion. Rowe et al. (p. 441; see the Perspective by Lewin) now show that grasshopper mice use the toxins present in the scorpion venom to block voltage-gated pain transmission, temporarily reducing their sensitivity to nonvenom-induced pain. Thus, grasshopper mice use the scorpions painful defense to their advantage and have evolved a mechanism that allows for reduction of pain sensitivity only when it is needed. Grasshopper mice use the scorpion’s strength against it—instead of inducing pain, scorpion venom blocks pain. [Also see Perspective by Lewin] Painful venoms are used to deter predators. Pain itself, however, can signal damage and thus serves an important adaptive function. Evolution to reduce general pain responses, although valuable for preying on venomous species, is rare, likely because it comes with the risk of reduced response to tissue damage. Bark scorpions capitalize on the protective pain pathway of predators by inflicting intensely painful stings. However, grasshopper mice regularly attack and consume bark scorpions, grooming only briefly when stung. Bark scorpion venom induces pain in many mammals (house mice, rats, humans) by activating the voltage-gated Na+ channel Nav1.7, but has no effect on Nav1.8. Grasshopper mice Nav1.8 has amino acid variants that bind bark scorpion toxins and inhibit Na+ currents, blocking action potential propagation and inducing analgesia. Thus, grasshopper mice have solved the predator-pain problem by using a toxin bound to a nontarget channel to block transmission of the pain signals the venom itself is initiating.

The rattling sound of rattlesnakes (Crotalus viridis) as a communicative resource for ground squirrels (Spermophilus beecheyi) and burrowing owls (Athene cunicularia)

Animal communication involves very dynamic processes that can generate new uses and functions for established communicative activities. In this article, the authors describe how an aposematic signal, the rattling sound of rattlesnakes (Crotalus viridis), has been exploited by 2 ecological associates of rattlesnakes: (a) California ground squirrels (Spermophilus beecheyi) use incidental acoustic cues in rattling sounds to assess the danger posed by the rattling snake, and (b) burrowing owls (Athene cunicularia) defend themselves against mammalian predators by mimicking the sound of rattling. The remarkable similarity between the burrowing owls defensive hiss and the rattlesnakes rattling reflects both exaptation and adaptation. Such exploitation of the rattling sound has favored alternations in both the structure and the deployment of rattling by rattlesnakes.

Isolation and Characterization of CvIV4: A Pain Inducing α- Scorpion Toxin

Background Among scorpion species, the Buthidae produce the most deadly and painful venoms. However, little is known regarding the venom components that cause pain and their mechanism of action. Using a paw-licking assay (Mus musculus), this study compared the pain-inducing capabilities of venoms from two species of New World scorpion (Centruroides vittatus, C. exilicauda) belonging to the neurotoxin-producing family Buthidae with one species of non-neurotoxin producing scorpion (Vaejovis spinigerus) in the family Vaejovidae. A pain-inducing α-toxin (CvIV4) was isolated from the venom of C. vittatus and tested on five Na+ channel isoforms. Principal Findings C. vittatus and C. exilicauda venoms produced significantly more paw licking in Mus than V. spinigerus venom. CvIV4 produced paw licking in Mus equivalent to the effects of whole venom. CvIV4 slowed the fast inactivation of Nav1.7, a Na+ channel expressed in peripheral pain-pathway neurons (nociceptors), but did not affect the Nav1.8-based sodium currents of these neurons. CvIV4 also slowed the fast inactivation of Nav1.2, Nav1.3 and Nav1.4. The effects of CvIV4 are similar to Old World α-toxins that target Nav1.7 (AahII, BmK MI, LqhIII, OD1), however the primary structure of CvIV4 is not similar to these toxins. Mutant Nav1.7 channels (D1586A and E1589Q, DIV S3–S4 linker) reduced but did not abolish the effects of CvIV4. Conclusions This study: 1) agrees with anecdotal evidence suggesting that buthid venom is significantly more painful than non-neurotoxic venom; 2) demonstrates that New World buthids inflict painful stings via toxins that modulate Na+ channels expressed in nociceptors; 3) reveals that Old and New World buthids employ similar mechanisms to produce pain. Old and New World α-toxins that target Nav1.7 have diverged in sequence, but the activity of these toxins is similar. Pain-inducing toxins may have evolved in a common ancestor. Alternatively, these toxins may be the product of convergent evolution.

Redesigning a General Education Science Course to Promote Critical Thinking

Traditional general education science courses appear ineffective at helping students improve their critical-thinking skills and engage with discomforting topics (e.g., evolution). A novel course focusing on the nature of science rather than the findings of science significantly overcame both deficiencies.

Meek males and fighting females: sexually-dimorphic antipredator behavior and locomotor performance is explained by morphology in bark scorpions (Centruroides vittatus).

Sexual dimorphism can result from sexual or ecological selective pressures, but the importance of alternative reproductive roles and trait compensation in generating phenotypic differences between the sexes is poorly understood. We evaluated morphological and behavioral sexual dimorphism in striped bark scorpions (Centruroides vittatus). We propose that reproductive roles have driven sexually dimorphic body mass in this species which produces sex differences in locomotor performance. Poor locomotor performance in the females (due to the burden of being gravid) favors compensatory aggression as part of an alternative defensive strategy, while male morphology is coadapted to support a sprinting-based defensive strategy. We tested the effects of sex and morphology on stinging and sprinting performance and characterized overall differences between the sexes in aggressiveness towards simulated threats. Greater body mass was associated with higher sting rates and slower sprinting within sexes, which explained the greater aggression of females (the heavier sex) and, along with longer legs in males, the improved sprint performance in males. These findings suggest females are aggressive to compensate for locomotor costs of reproduction while males possess longer legs to enhance sprinting for predator evasion and mate finding. Sexual dimorphism in the metasoma (“tail”) was unrelated to stinging and sprinting performance and may best be explained by sexual selection.

Donning your enemy's cloak: ground squirrels exploit rattlesnake scent to reduce predation risk

Ground squirrels (Spermophilus spp.) have evolved a battery of defences against the rattlesnakes (Crotalus spp.) that have preyed on them for millions of years. The distinctive behavioural reactions by these squirrels to rattlesnakes have recently been shown to include self-application of rattlesnake scent—squirrels apply scent by vigorously licking their fur after chewing on shed rattlesnake skins. Here, we present evidence that this behaviour is a novel antipredator defence founded on exploitation of a foreign scent. We tested three functional hypotheses for snake scent application—antipredator, conspecific deterrence and ectoparasite defence—by examining reactions to rattlesnake scent by rattlesnakes, ground squirrels and ectoparasites (fleas). Rattlesnakes were more attracted to ground squirrel scent than to ground squirrel scent mixed with rattlesnake scent or rattlesnake scent alone. However, ground squirrel behaviour and flea host choice were not affected by rattlesnake scent. Thus, ground squirrels can reduce the risk of rattlesnake predation by applying rattlesnake scent to their bodies, potentially as a form of olfactory camouflage. Opportunistic exploitation of heterospecific scents may be widespread; many species self-apply foreign odours, but few such cases have been demonstrated to serve in antipredator defence.

THE USE OF SOUTHERN APPALACHIAN WETLANDS BY BREEDING BIRDS, WITH A FOCUS ON NEOTROPICAL MIGRATORY SPECIES

Abstract Although loss of wetlands in southern Appalachia has been especially severe, no avian studies have been conducted in the vestiges of these ecosystems. Our research assessed avian use of southern Appalachian wetlands in the breeding seasons of 1999 through 2001. Site analyses included 18 habitat variables, including total wetland area, area of open water, beaver or livestock evidence, edge type (abrupt or gradual), and percent cover of nine vegetation types. We analyzed avian species richness and abundance at the community level and in guilds based on migratory status and breeding habitat preference. Measures of vegetation and habitat—particularly those resulting from beaver activities—and gradual edges were significantly correlated with guild- and community-level variables. Evidence of beaver (i.e., forest gaps where trees had been felled, ponds where drainages had been dammed; hereafter referred to simply as “beaver evidence”) was significantly correlated with greater community-level species richness and abundance. Both beaver evidence and gradual edge were positively associated with greater species richness and abundance of Neotropical migratory birds (NTMBs) overall, as well as with the late-successional NTMB guild. Presence of gradual edge alone also was significantly correlated with high abundance of birds in the early-successional NTMB guild. Beaver and gradual edge may have contributed to higher-quality breeding habitats with relatively greater overall productivity and structural complexity in some wetlands.